Multi-pane glazing structures have been in use for some time, since they have replaced single-pane windows, as thermally insulating windows, in industrial, commercial, and residential situations. Spacers used in the glazing structures have been made of aluminum, galvanized steel, plastic, polymer, rubber and other soft or hard materials, sometimes used alone and sometimes combined with each other. Spacer bars are set along the periphery of the space between the panes and are typically long hollow perforated metal sections. Aluminum alloy spacers (extruded or rolled from flat strip material) are still the most utilized spacers (other popular spacers are made of galvanized steel or silicone compound), due to low cost and ease of manufacturing. In most cases the hollow interior of the spacer contains a desiccant material which absorbs any moisture that may enter into the sealed unit and/or soak up any residual moisture that may have been in the enclosed air or low-conductive gas within the sealed unit.
Recent increases in energy costs as well as demand for a superior product have given rise to the need for windows and other multi-pane glazing structures of even higher thermal insulation ability.
To achieve what todays markets require, different approaches have been taken to increase the window's thermal insulation performance,
Additional panes have been incorporated into laminated structures, giving approximately R-1 for a single pane, R-2 for a double pane and R-3 for 3 or more panes. (Reference ASTM.)
Heat-reflective, low-emissivity ("low e") coatings have been incorporated into window structure. Special multi-pane glazing structure have been developed, as for example, in U.S. Pat. No 5,156,894 to Hood et al. (high performance, thermally insulating multi-pane glazing structure.)
Low heat transfer gas have been incorporated into the window structure. (to mention some: argon, krypton, nitrogen, etc.)
Spacers have evolved from steel and aluminum to lower coefficient of heat transfer material such as polymer plastic, fiberglass and rubber. The aim was to get away from metal spacers having too high of a thermal conductivity coefficient thus causing condensation on the inner surface of the multi-pane assembly when temperature is below the dew point. In most cases a high increase in cost of manufacturing render these products hard to market. Also a problem with reinforced plastic spacers was that they generally had a different coefficient of expansion than glass generating early failure of the sealed unit. Moreover, reinforced plastic spacers caused problems with permeability, either permitting vapor moisture to enter or the filling gas to escape. Generally one spacer assembly is made of four lengths of spacers mechanically fastened with corner joints, inserted under pressure. Other techniques include folding around the corner with or without notching the spacer or a complete cutting of the spacer after which the length of spacer is thermally welded or by other means jointed together without a mechanical joint. Once the panes have been put in place on each side of the spacer assembly, a sealant is applied to the outside of that particular assembly to seal and to adhere to the outermost area of the spacer frame and to the panes surface area facing the spacer frame and outside it.
Common sealing materials used for this type of assembly are generally made of compounds subject to undergoing polymerization by catalysis. These sealants are polysulfide derivatives of the urethane family. Polysulfide is used as a simple sealant or in combination with a primary sealant of the butyl family called poly-isobutylene. Polysulfide keeps its shape, elasticity and memory for great temperature differentials.
The inventors herein postulate some reasons for the limited access of better products in the markets. The inventors, however, do not wish to be bound by theory and are not specialists on market survey.
Most of the aforementioned methods to better insulating performance of window assemblies have increased the cost of manufacturing.
Most of the aforementioned methods to better insulating performance of window assembly have also increased the cost of materials.
Some of the aforementioned methods to better insulating performance of window assembly have additionally increased weight.